Former acting Attorney General Sally Yates has also cooperated with the special counsel, the network reported.

President Trump last year fired Yates from her post after she refused to defend his initial travel ban. She has since become a frequent critic of the Trump administration.

Pompeo and Director of National Intelligence Dan Coats, who has also spoken with Mueller's team, are "peripheral witnesses" to the firing of former FBI Director James Comey, one person familiar with the matter told NBC News.

The report comes one day after news broke that Attorney General Jeff Sessions was interviewed last week in the Mueller probe, which is investigating, among other things, possible connections between Trump's presidential campaign and Russia.

Sessions recused himself from the Russia investigation in March, despite criticisms from Trump. It was reported earlier this month that Trump ordered White House counsel Don McGahn to block Sessions from recusing himself, but the attorney general do so anyway.

Comey was also interviewed last year by Mueller's team.

Trump has repeatedly dismissed the Russia probe as a witch hunt and denied collusion.

Mueller reportedly wants to question Trump on his decision to fire Comey and the departure of his former national security adviser, Michael Flynn.

Two people familiar with Mueller's investigation told The Washington Post that Trump's legal team could present conditions for Trump to interview with Mueller's investigators as soon as next week.